3D shape measurement system based on fringe projection in 4-step phase shifting

In order to achieve the measurement of objects with significant jumping surface profile,a three-dimensional shape measurement system based on fringe projection in four-step phase shifting was established and the adopted four-step phase-shift measurement algorithm was studied. After introducing the principle of four-step phase shifting, a measurement algorithm for the apparent jumping faces was established, by taking a triangular pyramid rubber with significant jump faces for example. Firstly, the average gray image was calculated through a sum of the four phase shifting images and divided by four. Secondly,the binaryzation of average gray image was processed to position the obvious jumping surface or shadows. Last but not least, the convolution of binary image with wrapped phase map was done and then the wrapped phase map was unwrapped to get the correct continuous phase and reconstruct the 3D shape of the object. Experiments were taken to calculate the volume of the triangular pyramid rubber by shape measurement with the proposed algorithm. Experimental results show that the mean precision of volume measurement is 0.47%, which proves the effectiveness of the proposed algorithm and its good precision.